In general, an electric compressor has a lubricating mechanism at its shaft, and Japanese Patent Examined Publication No. S62-44108 discloses one of those instances. FIG. 5 shows a sectional view of this conventional compressor, and FIG. 6 shows an electric connection diagram of this compressor.
In FIG. 5, hermetic container 1 accommodates electric motor 4 formed of stator 18 and rotor 8, and compressing mechanism 2. Shaft 7 extends through bearing 6 of block 3, and rotor 8 of the motor is rigidly mounted to an outer wall of shaft 7, of which eccentric shaft 9 is coupled to piston 10 by slider 11. Shaft 7 includes centrifugal pump 12 formed at its lower end and opening into lubricant 17.
Shaft 7 includes spiral groove 14, engraved on its outer wall and having a lead, for leading lubricant 17 upward when the motor rotates in a predetermined forward direction. A lower end of spiral groove 14 communicates with centrifugal pump 12, and an upper end of spiral groove 14 communicates with annular lubricant groove 16 (not shown) formed on an upper end of bearing 6.
A lower end of vertical hole 15 bored in eccentric shaft 9 communicates with the annular lubricant groove 16, and an upper end of hole 15 opens into a space of hermetic container 1.
As shown in FIG. 6, stator 18 of the motor includes main coil 19 and starting coil 20. PTC (Positive Temperature Co-efficient) relay 21 is coupled to starting coil 20 in series, so that a resistance-start type of single-phase induction motor is formed.
Application of a voltage starts the motor rotating in a forward direction, and a temperature of elements of PTC relay 21 sharply rises, which accompanies a sharp increase in the resistance of the elements, so that starting coil 20 is actually cut off, and the motor is driven only by main coil 19. Lubricant 17 is sucked up to spiral groove 14 by centrifugal pump 12, and rotation of spiral groove 14 transports lubricant 17 upward for lubricating sliding sections of the compressor.
However, since the conventional electric compressor discussed above prepares the winding direction of the lead of the spiral groove 14 based on an assumption of a forward rotating direction, spiral groove 14 fails to transport the lubricant upward if the motor rotates in a reverse direction due to some reason. As a result, the sliding sections encounter no lubricant. This reverse rotation lasts until the compressor is stopped (max. several hours), and the motor returns to the forward rotation when the motor is re-started. However, abrasion sometimes occurs in the sliding sections during the reverse rotation.